Typically, an optical signal transported over an optical transport, such as an optical fiber or waveguide (hereinafter collectively optical transport) must be coupled from that optical transport to another optical transport or to an optoelectronic device. Thus, the end of the optical transport is assembled to an optical connector of a given form factor, e.g., MT, which connector can be coupled to a mating optical connector on the other optical transport or optoelectronic device.
Optical cables that are connected to each other through a pair of mating connectors may comprise a single optical transport. However, more and more commonly, optical cables contain a plurality of optical transports, and the light in each optical transport in the cable is coupled through a pair of mating connectors to a corresponding optical transport in another cable. Optical cables and connectors having more than 1000 transports or more are now available on the market.
In a typical optical fiber, for instance, the light is generally contained only within the core of the fiber, which typically may be about 10 microns in diameter for a single-mode fiber or about 50 microns in diameter for a multi-mode fiber. Waveguides are about equally as small in cross-sectional area, although they generally are rectilinear in cross-section (rectangular or square, rather than cylindrical). Accordingly, lateral alignment of the transports in one connector with the transports in the other connector must be very precise, such as on the order of 1-2 microns tolerances in order to assure that most of the light makes it through the connectors into the receiving transport. Hence, optical connectors generally must be fabricated extremely precisely to ensure that mating optical transports longitudinally align as well as possible so that as much light as possible is transmitted through the mating connectors to minimize signal loss during transmission.
Typically, an optical connector comprises a ferrule assembly that includes a separate cavity for each optical transport in the cable. Each optical transport is inserted into one of the cavities, which precisely aligns the transport laterally, i.e., horizontally and vertically (x and y planes) relative to some reference point on the ferrule assembly, such as an alignment pin and/or alignment hole that will mate with a corresponding alignment hole or pin on a mating connector. The optical transports will then be cut or polished flush with the front face of the ferrule assembly to make the ends of all of the transports coplanar (in the longitudinal or z direction).
The ferrule assembly then is placed in a connector housing that typically includes a mechanism for coarsely aligning the ferrules of two connectors when first mated and guiding the ferrules into engagement with the each other as well as a mechanism for releasably locking the two connectors together.
Such ferrules are commonly manufactured by injection molding and are relatively expensive and complex to manufacture because they have complex shapes and require significant polishing of many surfaces in order to achieve the desired tolerances. Typical tolerances for optical transport alignments are about 1-2 microns.